The onions start out piled high in the Dutch oven, but after a long, steady cook they collapse into a deep golden tangle that smells sweet and savory. I learned not to rush that part: pale onions make a much thinner, less rounded soup. In this French Onion Potato Soup, the onions bring the familiar slow-cooked flavor, while Yukon Gold potatoes turn the broth into something hearty enough to eat as a meal.
The soup gets its body without blending the whole pot. I mash about a third of the tender potato cubes right against the side of the pot, which thickens the broth and leaves plenty of soft pieces intact. A little cream smooths the finish, and Gruyere-topped baguette gives each bowl the crisp, bubbling top I want from French onion soup.
Give the onions time, then let the potatoes become very tender before mashing. You’ll end up with a rich, savory bowl and a cheesy toast ready to break into the soup.
Kitchen Note
Mash only about a third of the potatoes against the pot. That gives the broth a naturally thicker feel while leaving tender potato pieces in every spoonful; mashing much more changes the soup into a smoother, heavier bowl.
Save French Onion Potato Soup for a cozy dinner: deeply golden onions, tender potatoes, and a bubbling Gruyere toast on top.
Why the Onions Need More Time Than You Think
Two pounds of sliced onions look like an unreasonable amount when they first hit the pot. They release moisture as they cook, soften, and shrink down substantially. The 35–45 minutes isn’t idle time; it’s how the onions lose their raw bite and develop the deep, rounded flavor that carries this soup.
Keep the heat at medium, stir often, and lower it if you see the onions catching or darkening too quickly in spots. The goal is an even, deep golden color, not blackened edges. If the bottom of the pot gets too dark before the onions are soft, those scorched bits can make the finished broth taste bitter. The white wine helps loosen browned bits after the onions are cooked, but it won’t undo burnt flavor.
That slow onion base is what sets this apart from a potato soup with onions stirred in near the end. Once the broth and potatoes go in, the onion flavor spreads through the whole pot, and the potatoes soak it up as they simmer. Let the onions take the time they need before moving on.
How the Onion, Potato, and Gruyere Build the Bowl
- Yellow onions — Their balance of sweetness and savory flavor suits the long browning time. Slice them thinly so they soften at a similar pace; uneven, thick pieces are more likely to stay firm while the thinner ones darken.
- Yukon Gold potatoes — They cook up tender and have enough natural creaminess to help thicken the soup when mashed. Keep the cubes close to a 1/2-inch size so they soften evenly. Russets work, but break down more readily and make a softer, less distinct potato texture.
- Low-sodium beef broth — Beef broth gives the soup its savory, French-onion character, while a low-sodium version leaves more room to control the seasoning. Chicken broth works in a pinch, though the result tastes lighter and less deeply beefy.
- Dry white wine — It lifts the browned onion bits from the pot and adds a little acidity to balance the rich broth. Choose a dry wine you’d drink; if you don’t cook with wine, use broth in its place, knowing the soup will taste a little less bright.
- Heavy cream — A small amount softens the broth without turning it into a cream-heavy soup. Stir it in after the potatoes are tender, then keep the pot at a gentle simmer so the finish stays smooth.
- Gruyere and baguette — Gruyere melts into a savory, bubbling cap, while baguette slices hold their shape under the cheese. Freshly shredded cheese melts more evenly than many pre-shredded blends. Swiss cheese is a workable substitute, with a slightly milder flavor.
Build the Soup in Stages, Then Broil the Toast
Cook the Onions Until Deeply Golden
Melt the butter with the olive oil in a 6-quart Dutch oven over medium heat, then add the thinly sliced onions, salt, and pepper. Stir often as they soften and reduce, lowering the heat if they start to scorch. This takes 35–45 minutes; look for onions that are deeply golden and much smaller in volume. Don’t move on while they’re still pale and sharply oniony.
Bloom the Garlic and Deglaze the Pot
Stir in the minced garlic and dried thyme and cook for 30 seconds, just until fragrant. Sprinkle in the flour and stir for 1 minute so it coats the onions rather than forming dry clumps. Pour in the white wine and scrape across the bottom of the pot to release the browned bits. Let it simmer for 2–3 minutes, until nearly evaporated, before adding the broth.
Simmer the Potatoes Until Very Tender
Add the beef broth, cubed potatoes, and bay leaf, then bring the pot to a boil. Reduce the heat and simmer for 15–20 minutes, until a fork passes easily through a potato cube. If the pieces still feel firm in the center, give them more time before mashing; firm potatoes won’t break down smoothly against the side of the pot. Mash about one-third of the potatoes, then stir in the cream and simmer gently for 2 minutes before removing the bay leaf.
Toast the Baguette and Melt the Gruyere
Heat the oven to 425°F with a rack in the upper third. Arrange the baguette slices on a rimmed baking sheet and bake, turning once, for 6–8 minutes, until crisp and lightly golden. Sprinkle Gruyere over the slices, then broil on high about 6 inches from the heating element for 1–2 minutes. Stay close: the cheese goes from bubbling to over-browned quickly under the broiler.
Easy Changes for a Different Bowl
Make It Gluten-Free
Omit the all-purpose flour and leave the rest of the soup method unchanged. The mashed Yukon Gold potatoes still give the broth body, though it will be a little less velvety. Use gluten-free baguette for the cheesy toasts, or skip the toast and serve the soup on its own.
Use Swiss Instead of Gruyere
Top the baguette with shredded Swiss cheese in place of Gruyere and broil it the same way. Swiss melts well and keeps the toast savory, but its flavor is milder, so the cheese won’t stand out as strongly against the deeply cooked onions.
Storage and Reheating
- Refrigerator: Store the soup in a covered container for 3–4 days. The potatoes will continue to soften and the soup may thicken as it chills.
- Freezer: Freeze the soup before adding the cream for up to 2 months. Cool it promptly, portion it into freezer-safe containers, and expect the potatoes to soften after thawing. Thaw overnight in the refrigerator, reheat gently, then stir in the cream and simmer for 2 minutes.
- Reheating: Warm refrigerated soup on the stovetop over low to medium-low heat, stirring occasionally. Avoid a hard boil after the cream is in; high heat can make the texture less smooth. Store the cheesy toasts separately and make them fresh for serving.
Questions That Come Up When Making This Soup
French Onion Potato Soup
Ingredients
Equipment
Method
- Melt the butter with the olive oil in a 6-quart Dutch oven over medium heat.
- Add the onions, salt, and pepper, then cook, stirring often and lowering the heat if they begin to scorch, until the onions are deeply golden and reduced, 35–45 minutes.
- Stir in the garlic and thyme and cook for 30 seconds.
- Sprinkle in the flour and stir for 1 minute.
- Pour in the white wine and scrape up the browned bits from the bottom of the pot; simmer until nearly evaporated, 2–3 minutes.
- Add the beef broth, potatoes, and bay leaf, bring to a boil, then reduce the heat and simmer until the potatoes are very tender, 15–20 minutes.
- Mash about one-third of the potatoes against the side of the pot with a potato masher to thicken the soup.
- Stir in the heavy cream and simmer gently for 2 minutes.
- Remove the bay leaf.
- Heat the oven to 425°F and arrange a rack in the upper third.
- Place the baguette slices on a rimmed baking sheet and bake, turning once, until crisp and lightly golden, 6–8 minutes.
- Sprinkle the Gruyere over the toasted bread and broil on high, about 6 inches from the heating element, until the cheese is melted and bubbling, 1–2 minutes.
- Ladle the soup into bowls and top each serving with a cheesy toast.
